The invention relates to methods of producing flexible, vulcanizable composite tubing for applications in a hydraulic system that employs a non-combustible, force-transmitting fluid. The invention also relates to tubing produced by such methods.
Hydraulic systems which employ, as the force-transmitting medium, a non-combustible liquid (e.g., liquids derived from phosphate esters) are by nature much less hazardous than systems employing petroleum-based hydraulic fluids, which are highly flammable. The use of systems employing such non-combustible fluids, has the disadvantage of severely complicating the construction of the flexible tubing elements that must be present in such systems to compensate relative movement of the force-transmitting and force-receiving elements. Such complication arises from the fact that the rubber-type substance which must be embedded in the steel insert that forms the load-bearing interior layer of such tubes to form an efficient bond therewith, is damaged by contact with the phosphate esters forming the base of the non-corrosive hydraulic fluid.
On the other hand, substances such as ethylene-propylene-terpolymer (EPDM) rubber and natural rubber, which are essentially impervious to the phosphate esters in the hydraulic fluid, are incapable of forming, with metal inserts of the flexible tube, the required bond necessary to assure structural integrity and efficient operation of the tube.